Emma Townshend: 'Peonies paling? Daffs drooping? Then turn to flowers that bloom all summer long'

July is prime time for reconsidering what you've got growing, says our gardening correspondent

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Gardening is a confusing business. For example, there's that classic puzzled beginner's face which arises when, after being purchased in full glorious bloom, some flowers promptly shut up shop until the following June. "What is this enormous swizz?" the beginner gardener asks. And rightly so.

The problem arises because some good-natured members of the plant kingdom – geraniums, daisies, fuchsias – create unreal expectations for everything else by flowering continuously as long as it's sunny. In contrast, the other half of the floral world – delphiniums, peonies or daffodils, say – flower for a moment in the year, and once they're done, they don't repeat for 12 months.

This enormous distinction causes all kinds of heartbreak among beginners. "My peony is DYING," they wail, "all its lovely flowers have fallen off." We can only hope it's a relief to know that it's not actually their fault at all; it's just life being annoyingly seasonal.

July marks the moment when that seasonal spring and early-summer flowering – the daffs and peonies – concludes. As a result, it's prime time for reconsidering what you've got growing. And then sticking in a load of the "would flower forever if permitted" lot. This rule applies whether you have a huge 100ft country-house border or one lone container perched dodgily on a new-build Juliet balcony.

For me, it's also a good moment to have fun with big leaves, exotic planting and bright colours. I'd probably begin with the giant foliage. Every year, cannas and banana plants, with their huge green sail leaves, seem to become more widely available as they become more popular. They need good sunshine and lots of water to get established (though after a few years, mine are now fully settled and I never water them at all).

Both bananas and cannas can acclimatise themselves to city gardens, clumping up with bulblets, which gets them going quickly in spring, and they also do well in pots as long as you keep an eye on the water. And cannas will flower continuously until first frost with hilariously gaudy blooms – and a parrot-like flourish at the top – as long as you take off the seedheads as they start to form.

Another off-the-scale exotic is the Datura, a hallucinogenic plant from South America often nicknamed Angel's Trumpets – though it should be kept well away from any of your own little angels, whether children or cats: they are spectacularly quick growers once they get going – I've had a 6ft plant within a single summer – bearing many horribly poisonous trumpets. Yet, despite toxicity levels through the roof, their perfume is seductive, from gigantic yellow, pink or white flowers. Frankly, bonkers.

Next stop is the daisy family: from marigolds to dahlias, these are often co-operative performers. Cosmos is a brilliant choice for small front-garden patches, pots and gigantic border gaps alike, as it seems to expand into whatever space is available. They just need a bit of help to get beyond slug-fodder size. I also like Marguerites, which look like giant lawn daisies and flower with formidable energy through my laziest time of the year.

Finally, there's the tequila plant, the agave (pictured), a spiky rosette of grey-green leaves that brings a touch of the Arizona desert to suburban England. These plants do surprisingly well, accustomed as they are to cold desert nights: you just have to stop them rotting at the base by planting in grit and removing dead leaves that fall around them. They are probably best off in pots. Easy plants, all, to make even a beginner feel expert.

Four more plants with stamina

Cosmos 'Chocamocha'

Chocolate-scented, with velvety, dark-brown flowers that last until at least September. Great for growing in a sunny border. £6.99, crocus.co.uk

Musa basjoo

Their huge, paddle-like blue-green leaves, which can grow up to 3m each, mean they're an extraordinary sight in any garden. £19.99, crocus.co.uk

Agave americana

Can cope with below-zero temperatures in winter. A small plant will eventually produce offshoots if you treat it kindly. £17.50, burncoose.co.uk

Datura versicolor

Should be planted in good soil in a big pot and fussed over, for full psychotropic horticultural effect from May to September. £13, burncoose.co.uk